The lower projection is based on a mercury rise of two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels -- the warming ceiling the world's nations agreed on in 2015.
The highest is for out-of-control warming of 4.5 C.
"Global biodiversity will suffer terribly over the next century unless we do everything we can," said conservation group WWF, which commissioned the analysis published in science journal Climatic Change.
"We must keep average global temperatures down to the absolute minimum."
The report focused on 33 so-called "Priority Places" which host some of the world's richest and most unusual terrestrial species, including iconic, endangered, or endemic plants and animals.
They include southern Chile, the eastern Himalayas, South Africa's unique Fynbos ecoregion, Borneo, Sumatra, the Namibian desert, West Africa, southwest Australia, coastal east Africa, and southern Africa's Miombo Woodlands, home to African wild dogs.
The team looked at the impact of climate change on nearly 80,000 terrestrial plant, mammal, bird, amphibian, and reptile species.
At warming of 4.5 C, based on a "business-as-usual" scenario of no emissions cuts, the Amazon could risk the local extinction of 69 percent of its plant species.
The Miombo Woodlands risks losing 90 percent of its amphibians, 86 percent of birds, and 80 percent of mammals, according to the report.
Under the 2015 Paris Agreement, countries made voluntary pledges to curb planet-warming greenhouse gas emissions from burning coal, oil and natural gas.